Mario Vittone posted some comments on his blog about whether the Ocean Signal unit might be actually be too small. Note that he is refering specifically to use in a marine environment, like in a lifejacket pocket. His concerns might not be as significant for use when climbing or backpacking. He has obtained one to test and has promised a follow up evaluation, but so far I haven't see it.

Vittone is a former USCG Rescue Swimmer, now retired. He was one of the volunteers in the Cold Water Boot Camp videos.